Etching method, etching apparatus and storage medium

ABSTRACT

An etching method for forming a groove by etching a silicon layer of a substrate by using a mask which has a first region where an opening with a first opening width is formed and a second region where an opening with a second opening width larger than the first opening width is formed, the method includes: mounting the substrate on a mounting table in a processing chamber; converting a processing gas containing Cl 2  gas, HBr gas, and one of CO gas and CO 2  gas into a plasma; and etching the silicon layer by the plasma.

FIELD OF THE INVENTION

The present invention relates to a technique for plasma etching a singlecrystalline silicon layer or a polycrystalline silicon layer.

BACKGROUND OF THE INVENTION

In manufacturing semiconductor devices, there is a plasma etchingprocess of a silicon layer. To be specific, there is an etching processfor etching single crystalline silicon to form a groove for burying anoxide film serving as a device isolation film or an etching process foretching polysilicon, i.e. polycrystalline silicon, to form a recess forembedding the oxide film while leaving a gate electrode.

FIGS. 7A to 7C illustrate a process of forming a groove-like space 105,i.e. a recess for burying a device isolation film in a silicon layer 100of a substrate 101. The silicon layer 100 is etched through a hard mask102 made of silicon nitride. As shown in FIG. 7A, the hard mask 102 hasgroove-type openings 103 whose dimension is S and protruded portions 104between adjacent openings 103 whose dimension is L. Further, the hardmask 102 of the same substrate 101 has a dense pattern region where thedimension S is small and the neighboring protruded portions 104 aredensely arranged and a sparse pattern region where the dimension S islarge and the neighboring protruded portions 104 are spaced apart fromeach other.

If the substrate 101 is etched by using a processing gas, e.g., Cl₂ gas,by-products containing, e.g., silicon and chlorine are generated. Someof the by-products are vaporized and discharged from the openings 103,but the rest of them are deposited as deposits 106 on the sidewallindicated as lines 107 between the spaces 105, as shown in FIG. 7B.Since the dimension of the lines 107 is getting larger due to this, thedimension S′ of the spaces 105 after the etching process becomes smallerthan the dimension S of the openings 103 formed through the hard mask102, as shown in FIG. 7C.

Meanwhile, if the hard mask 102 has the dense and sparse pattern regionsof the protruded portions 104 as described above, the volume of onesingle recess (opening) 103 in the sparse pattern region is larger thanthat in the dense pattern region. Therefore, more by-products aregenerated in a single recess of the sparse pattern region than in asingle recess of the dense pattern region. Further, since the amount ofthe deposits 106 increase as the amount of the by-products increase, theamounts of the deposits 106 in the sparse pattern region are larger thanthose in the dense region.

As a result, the sidewall tilt angle β of the lines 107 in the sparsepattern region is smaller than the sidewall tilt angle α of the lines107 in the dense pattern region, as shown in FIG. 7C. As the differenceof the dimensions S of the openings 103 in the dense and sparse patternregions increases, the amount of the difference of the generatedby-products becomes larger, which results in the increase of thedifference between the sidewall tilt angles α and β of the lines 107.Furthermore, since the deposits 106 are more easily deposited in thesparse pattern region than in the dense pattern region, if the amountsof the by-products increase, the difference between the sidewall tiltangles α and β of the lines 107 in the dense and sparse pattern regionsincreases, as shown in FIG. 8.

If the sidewall tilt angles α and β of the lines 107 after the etchingprocess in the dense and sparse pattern regions are unbalanced asmentioned above, and then for example, if the hard mask 102 is removedand an oxide film is embedded in the space 105, burying properties(filling rate) of the oxide film in the space 105 of the oxide filmcannot be uniform. Moreover, if the filling rate of the oxide film isnot uniform, electrical characteristics such as oxide film withstandingvoltage characteristics may also not be uniform in surface. Therefore,it is required to make the sidewall tilt angles α and β of the lines 107in the dense and sparse pattern regions equal to each other.

Conventionally, the etching process is performed under the processingconditions controlled such that the deposits 106 are prevented to bedeposited on the sidewall of the lines 107 or the deposits 106 are to beremoved. That is, the processing conditions are adjusted so that thesidewall tilt angles α and β of the lines 107 are very large (close to90°) and thereby the difference between the sidewall tilt angles α and βof the lines 107 in the dense and sparse pattern regions becomes small.

However, since it is preferable that the sidewall tilt angles α and β ofthe lines 107 are small, i.e. reclined, for the enhancement of theburying properties of the oxide film described above, it is required tomake the sidewall tilt angles α and β in the dense and sparse patternregions equal to each other and at the same time to make the tilt anglesα and β small. Furthermore, techniques for freely controlling thesidewall tilt angles α and β of the lines 107 are also required.

Japanese Patent Laid-open Application No. 1996-115900 (paragraphs [0021]and [0022]) discloses a technique for etching a silicon-based layer intoa groove shape by using Cl₂ gas and CO gas, but the difference in shapeof grooves or the tilt angles of the lines 107 in the dense and sparsepattern regions are not considered.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a technique capableof making sidewall tilt angles of protruded portions between openingssmall and making the sidewall tilt angles become equal in surface whenforming grooves by etching a single crystalline silicon layer or apolycrystalline silicon layer through a mask where openings havedifferent opening widths.

In accordance with a first aspect of the present invention, there isprovided an etching method for forming a groove by etching a siliconlayer of a substrate by using a mask which has a first region where anopening with a first opening width is formed and a second region wherean opening with a second opening width larger than the first openingwidth is formed, the method including: mounting the substrate on amounting table in a processing chamber; converting a processing gascontaining Cl₂ gas, HBr gas, and one of CO gas and CO2 gas into aplasma; and etching the silicon layer by the plasma.

Preferably, protruded portions between grooves are densely arranged inthe first region and are less densely arranged in the second region thanin the first region.

The mask may be formed of a silicon nitride film.

Further, the mask also may be patterned such that a ratio of the secondopening width to the first opening width is about 6 or more.

Preferably, etching the silicon layer is performed by converting theprocessing gas into the plasma by supplying high frequency power betweenan upper electrode which is disposed above the substrate to face it anda lower electrode serving as a part of the mounting table.

In accordance with a second aspect of the present invention, there isprovided an etching apparatus for forming a groove by etching a siliconlayer of a substrate by using a mask which has a first region where anopening with a first opening width is formed and a second region wherean opening with a second opening width larger than the first openingwidth is formed, the apparatus including: a mounting table disposed at alower portion of a processing chamber; a gas supply line for supplying aprocessing gas containing Cl₂ gas, HBr gas, and one of CO gas and CO₂gas to the processing chamber; and a plasma generator for converting theprocessing gas into a plasma.

Preferably, the plasma generator includes an upper electrode which isdisposed above the substrate to face it and a lower electrode serving aspart of the mounting table.

In accordance with a third aspect of the present invention, there isprovided a storage medium storing therein a computer program executableon a computer, the computer program being used in an etching apparatusfor forming a groove by etching a silicon layer of a substrate by usinga mask which has a first region where an opening with a first openingwidth is formed and a second region where an opening with a secondopening width larger than the first opening width is formed, wherein thecomputer program is configured to execute the etching method describedabove.

In accordance with the present invention, in case of forming grooves byetching the single crystalline silicon layer or a polycrystallinesilicon layer through a mask where the opening widths of the openingsare different, the etching process is performed by using the processinggas containing a gas selected from Cl₂ gas, HBr gas, CO gas and CO₂ gas.Therefore, plasma containing carbon increases, whereby the difference inamounts of the deposits caused by the different opening widths of theopenings of the mask is relatively reduced. Accordingly, the sidewalltilt angles of the protruded portions between openings become smaller,and further, they can be uniform in surface of the substrate.Furthermore, the sidewall tilt angles of the protruded portions can befreely controlled by adjusting the amount of the carbon plasma bychanging the flow rate of CO gas or CO₂ gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become apparentfrom the following description of embodiments given in conjunction withthe accompanying drawings, in which:

FIGS. 1A to 1C show cross sectional views of an exemplary wafer W usedin an etching process in accordance with the present invention;

FIG. 2 shows a longitudinal cross sectional view of an exemplary etchingapparatus used in the etching process;

FIGS. 3A and 3B are characteristic graphs showing results in accordancewith an embodiment of the present invention;

FIG. 4 is a characteristic graph showing results in accordance with theembodiment of the present invention;

FIG. 5 is a cross sectional view of a wafer W used in the embodiment ofthe present invention;

FIG. 6 is a characteristic graph showing results in accordance with theembodiment of the present invention;

FIGS. 7A to 7C are cross sectional views of a substrate used in aconventional etching process; and

FIG. 8 shows a characteristic graph showing a correlation between theamounts of by-products and the sidewall tilt angles in the etchingprocess.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings which form a parthereof.

An exemplary semiconductor substrate (hereinafter, referred to as a“wafer W”) on which an etching method of the present invention isapplied will be described with reference to FIGS. 1A to 1C. On a siliconlayer 11 of the wafer W shown in FIG. 1A, an oxide film 12 of athickness of, e.g., 10 nm and a SiN (silicon nitride) film 13 of athickness of, e.g., 100 nm, are formed in that order from the bottomside. Further, the oxide film 12 and the SiN film 13 are provided withprotruded portions 15 and groove-type openings 16, so that patternshaving spaces 14 and lines 17 can be formed in the silicon layer 11 byusing the oxide film 12 and the SiN film 13 as a hard mask.

Furthermore, the oxide film 12 and the SiN film 13 in the same wafer Ware provided with a first region, i.e. a dense pattern region in whichthe dimension of an opening 16 is as small as the first opening width S1so that the distance between the protruded portions 15 is small and theprotruded portions 15 are densely arranged, and a second region, i.e. asparse pattern region in which the dimension of an opening 16 is as wideas the second opening width S2 so that the distance between theprotruded portions 15 is large and the protruded portions 15 aresparsely arranged. For example, the first opening width S1 and thesecond opening width S2 are respectively 160 nm and 1100 nm. Further,the dimensions L of the protruded portions 15 in the dense and sparsepattern regions are respectively 100 nm and 110 nm. The wafer W isetched in the following manner by an etching apparatus 51, which will bedescribed later, to form the space 14 for burying an oxide film fordevice isolation as a part of an STI process.

Etching of Silicon Layer 11

As a processing gas for the wafer W, e.g., Cl₂ gas, HBr gas and CO gasare supplied, e.g., at flow rates of 65, 35 and 20 sccm, respectively.Subsequently, the processing gas is converted into plasma, which will bedescribed later. By supplying the plasma to the wafer W, the siliconlayer 11 is etched by using the oxide film 12 and the SiN film 13 as amask. At that time, since the opening widths S1 and S2 of the openings16 in the dense and sparse pattern regions are different from eachother, the etching amount of the silicon layer 11 in each opening 16 isdifferent. In other words, since the etching amount in the sparsepattern region is larger than that in the dense pattern region, theamounts of by-products generated in the sparse pattern region are largerthan those in the dense pattern region.

Besides, by supplying CO gas as a part of the processing gas, carbonplasma increases so that the amount of difference between theby-products generated in the dense and sparse pattern regions can beignorable. Therefore, as shown in FIG. 1B, the amounts of the deposits18 deposited on the sidewalls of the lines 17 in the dense and sparsepattern regions are almost same. Consequently, as the etching of thesilicon layer 11 is being performed, the spaces 14 in the dense andsparse pattern regions are formed to have dimensions slightly smallerthan the opening widths S1 and S2, respectively. That is, the etching iscarried out so that angles between the sidewalls of the lines 17 and ahorizontal plane (tilt angles) can be specific angles α and β. Asdescribed above, since almost same amounts of deposits 18 are depositedon the sidewalls of the lines 17 in the dense and sparse patternregions, the tilt angles α and β of the lines 17 are substantially thesame as those shown in FIG. 1C. Moreover, the spaces 14 having a desireddepth of, e.g., 250 nm are formed. Thereafter, the oxide film 12 and theSiN film 13 are removed and an oxide film for device isolation is buriedin the spaces 14.

Etching Apparatus

Hereinafter, an example of an etching apparatus 51 used in the etchingprocess will be described with reference to FIG. 2. The etchingapparatus 51 includes a processing chamber 21 formed of a vacuumchamber, a mounting table 30 disposed at a lower central portion in theprocessing chamber 21 and an upper electrode 40 provided above theprocessing chamber 21. A gas exhaust unit 23 including a vacuum pump orthe like is connected to a gas exhaust port 22 formed in the bottomsurface of the processing chamber 21 via a gas exhaust line 24. Formedthrough a sidewall of the processing chamber 21 is a transfer opening 25for a wafer W, which is closed and opened by a gate valve 26. Theprocessing chamber 21 is grounded.

The mounting table 30 includes a lower electrode 31 and a supportingbody 32 supporting the lower electrode 31 from the bottom, and it isdisposed on a bottom portion of the processing chamber 21 via aninsulation member 33. An electrostatic chuck 34 is provided on themounting table 30, and the wafer W is electrostatically attracted to beadsorbed to the mounting table 30 by a voltage applied to theelectrostatic chuck 34 from a high voltage DC power supply 35. Formed inthe mounting table 30 is a temperature control medium path 37 throughwhich a specified temperature control medium flows, the wafer W beingcontrolled to be maintained at a desired temperature by the temperaturecontrol medium. Further, formed in the mounting table 30 is a gaschannel 38 for supplying thermally conductive gas such as He gas or thelike as the backside gas. The gas channel 38 is opened at plurallocations on the top surface of the mounting table 30. These openingportions communicate with through-holes 34 a formed in the electrostaticchuck 34.

The lower electrode 31 is grounded via a high pass filter (HPF) 30 a,while a high frequency power supply 31 a of, e.g., 13.56 MHz isconnected to the lower electrode 31 via a matching unit 31 b.Furthermore, a focus ring 39 is disposed on an outer peripheral portionof the lower electrode 31 to surround the electrostatic chuck 34, sothat the plasma generated is to be converged toward the wafer W on themounting table 30 through the focus ring 39.

The upper electrode 40 has a hollow shape and a plurality of holes 41through which the processing gas is dispersedly supplied into theprocessing chamber 21 is uniformly formed at the bottom surface of theupper electrode 40, which forms a gas shower head. Further, a gasintroduction line 42 serving as a gas supply line is connected to acentral portion of the top surface of the upper electrode 40, while itpasses through the central portion of the upper wall of the processingchamber 21 via an insulation member 27.

Further, the upstream side of the gas introduction line 42 is dividedinto five branch lines 42A to 42E, ends of which are respectivelyconnected to gas supply sources 45A to 45E via valves 43A to 43E andmass flow controllers 44A to 44E. The valves 43A to 43E and the massflow controllers (MFCs) 44A to 44E form a gas supply system 46.Furthermore, the upper electrode 40 is grounded via a low pass filter(LPF) 47, while it is connected to a high frequency power supply 40 awith a frequency of, e.g., 60 MHz higher than that of the high frequencypower supply 31 a via a matching unit 40 b.

The high frequency power from the high frequency power supply 40 acoupled to the upper electrode 40 is to convert the processing gas intoplasma. The high frequency power from the high frequency power supply 31a coupled to the lower electrode 31 is to apply a bias power to thewafer W and to attract ions in the plasma to the surface of the wafer W.The upper electrode 40 and the lower electrode 31 serve as a plasmagenerator.

Further, the etching apparatus 51 includes a controller 20A formed of,e.g., a computer, the controller 20A having a data processing unitformed of a program, a memory and a CPU. The program has commandsrepresenting processing or transfer of the wafer W by which thecontroller 20A sends control signals to each part of the etchingapparatus 51 to perform a corresponding step which will be describedlater. Furthermore, the memory is provided with areas where processingparameters such as processing pressure, processing time, a gas flowrate, power and the like are recorded.

Therefore, if the CPU executes the commands of the program, theprocessing parameters are read out and control signals corresponding tothe parameters are transmitted to respective parts of the etchingapparatus 51. The program, which includes a program related to inputmanipulation or display of the processing parameters, is stored in acomputer-readable storage medium 20B such as a flexible disc, a compactdisc, a MO (magneto-optical disc), a hard disc and the like and isinstalled in the controller 20A.

Hereinafter, there will be described an etching method using the etchingapparatus 51 described above. First, a wafer W is horizontally mountedon the mounting table 30 in the processing chamber 21 by a substratetransfer mechanism (not shown) and the gate valve 26 is closedthereafter. Subsequently, the backside gas is supplied from the gaschannel 38 so that the wafer W is set to be maintained at apredetermined temperature.

After that, the gas exhaust unit 23 evacuates the inside of theprocessing chamber 21 through the gas exhaust line 24 to maintain thepressure in the processing chamber 21 at 3.3 Pa (25 mTorr), and Cl₂ gas,HBr gas and CO gas serving as the processing gas are supplied from thegas supply system 46 at gas flow rates of 65 sccm, 35 sccm and 20 sccm,respectively. Subsequently, the high frequency power with a frequency of60 MHz and a power of, e.g., 500 W is applied to the upper electrode 40to convert the processing gas into plasma. At the same time, the highfrequency power with a frequency of 13.56 MHz and a power of, e.g., 200W as the bias power is applied to the lower electrode 31. The siliconlayer 11 is etched by the generated plasma, as described above.

If the silicon layer 11 is etched by Cl₂ gas and HBr gas, the openingwidth S2 of the openings 16 in the sparse pattern region is larger thanthe opening width S1 of the openings 16 in the dense pattern region andthe amount of by-products generated in the sparse pattern region islarger than those generated in the dense pattern region. However, inaccordance with the embodiment described above, since CO gas containingcarbon is supplied to form the plasma including carbon, the carbonplasma is generated and the amount thereof is increased so much that thedifference between the amounts of the generated by-products can beignorable. Accordingly, almost the same amounts of deposits 18 aredeposited on the sidewalls of the lines 17 in the dense and sparsepattern regions, so that the sidewall tilt angles α and β of the lines17 can be small and substantially identical.

Moreover, the amounts of the deposits 18 can be adjusted by adjustingthe amount of the carbon plasma by changing the flow rate of CO gas,whereby the sidewall tilt angles α and β of the lines 17 in the denseand sparse pattern regions can be matched to each other, and further thesidewall tilt angles α and β in surface of the wafer W can be freelyadjusted.

Furthermore, since Cl₂ gas and HBr gas are used together to etchsilicon, the process characteristics such as an etching rate can beprecisely controlled. To be specific, although Cl₂ gas as well as HBrgas can be used to etch the silicon, reaction product of Cl₂ gasgenerated by the etching has a low vapor pressure and therefore theetching rate thereof is higher than that of HBr gas. For this reason,using HBr gas and Cl₂ gas which have different etching rates andcontrolling respective flow rates (partial pressure) thereof makeprecise control of the process easier than individually using each gas.

Furthermore, while the etching method of the present invention isapplied to the process for forming the spaces 14 in the silicon layer 11through the mask where the opening widths S1 and S2 of the openings 16are different, it is highly effective if the difference between theopening widths S1 and S2 is large, for example, if a ratio of theopening width S2 in the sparse pattern region to the opening width S1 inthe dense pattern region is 6 or more. To be more specific, a lot ofdeposits 18 are needed to make the tilt angles α and β small (reclined).However, if there is a large difference between the opening widths S1and S2, the difference between the amounts of the deposits 18 in thedense pattern region and in the sparse pattern region is significantlylarge according to the conventional method, as described with referenceto FIG. 8, thereby making it impossible to form a space 14 where thedifference of the tilt angles α and β is small.

On the contrary, in accordance with the present invention, the amountsof the deposits 18 can be controlled to be nearly uniform in surface ofthe wafer W by increasing the amount of the carbon plasma. Therefore,even in case of the wafer W where there is a large difference betweenthe opening widths S1 and S2, it is possible to etch the wafer W suchthat the sidewall tilt angles α and β of the lines 17 are nearly thesame. Moreover, since the amount of the carbon plasma can be increasedby controlling the flow rates of CO gas or CO₂ gas such that thedifference of the amounts of the by-products generated corresponding tothe difference of the opening widths S1 and S2 of the openings 16 isignorable, the etching method of the present invention can be applied toany wafer W regardless of the above ratio.

Although the above embodiment has been described with the singlecrystalline silicon layer 11, the etching method of the presentinvention may be applied to polycrystalline silicon, as will bedescribed in the following example. As for the processing gas, CO₂ gasmay be used instead of CO gas, as will be described in the followingexample. Further, dilution gas such as nitrogen gas or argon gas may besupplied along with the above gas as the processing gas, and oxygen gasmay also be supplied.

EXAMPLES Example 1

Next, an experiment of the etching method in accordance with the presentinvention will be described. In the experiment, the silicon layer 11 ofthe wafer W shown in FIG. 1 was etched by the etching apparatus 51 underthe following conditions in order to confirm the influence of the flowrate of CO gas. Thereafter, the wafer W was cut, and the sidewall tiltangles α and β of the lines 17 in the dense and sparse pattern regionswere measured. Further, by measuring the depth of the spaces 14, anetching rate and micro-loading indicated as a ratio of the depth of thespace 14 in the sparse region to the depth of the space 14 in the denseregion were calculated. Further, the etching rate was derived from anaverage of etching rates in the dense and sparse pattern regions.

[Processing Conditions]

Processing pressure: 3.3 Pa (25 mTorr)

Frequency of the high frequency power of the upper electrode 40: 60 MHz

Power of the upper electrode 40: 500 W

Frequency of the high frequency power of the lower electrode 31: 13.56MHz

Power of the lower electrode 31: 200 W

Example 1-1

Processing gas: Cl₂/HBr/CO=65/35/10 sccm

Example 1-2

Processing gas: Cl₂/HBr/CO=65/35/20 sccm

Comparative Example 1

Processing gas: Cl₂/HBr=65/35 sccm

Experimental Result

As shown in FIG. 3A, it is noted that the sidewall tilt angles α and βof the lines 17 in the dense and sparse pattern regions are becomingequal to each other as the flow rate of CO gas increases. Furthermore,it is also noted that the sidewalls of the lines 17 are not close to thedirection perpendicular to the surface plane, i.e. the tilt angles α andβ are not close to 90°, but they are close to the surface plane, i.e.the tilt angles α and β become small.

On the other hand, the etching rate and the micro-loading are degradedby the addition of CO gas, as shown in FIG. 3B. That is, by adding COgas, the etching rate slightly decreases and the micro-loading slightlyincreases, i.e. the depth of the space 14 in the dense pattern region isreduced. The reason for this is probably that the amount of the carbonplasma increases by the addition of CO gas so that the deposits 18 onthe bottom surface of the space 14 increase, as described above. Thatis, since the opening width S1 of the openings 16 in the dense patternregion is narrow, by-products gene N by the etching are hardlydischarged outside, and therefore they seem to become the deposits 18.However, such a side effect caused by the addition of CO gas isimmaterial since the added amount thereof is only about 10% or less inthe experiment.

Example 2

The same experiment as that of the example 1 was carried out under thefollowing conditions except that CO₂ gas was used instead of CO gas.Further, any description on the same conditions as those in the example1 will be omitted here.

Example 2-1

Processing gas: Cl₂/HBr/CO₂=65/35/20 sccm

Example 2-2

Processing gas: Cl₂/HBr/CO₂=65/35/40 sccm

Comparative Example 2

Processing gas: Cl₂/HBr=65/35 sccm

Experimental Result

As shown in FIG. 4, the result of this experiment is the same as theresult of the example 1. Although the results of the etching rate andthe micro-loading are not shown, the degradation in this experiment wasonly 10% even if the flow rate of CO₂ was up to 40 sccm. That is, inthis experiment, the flow rate of CO₂ gas was able to be increased up totwice that of CO gas in example 1, which resulted in that the absolutevalues of the tilt angles α and β in the dense and sparse patternregions became further decreased. It is considered most likely due tothe influence of plasma containing oxygen after CO₂ gas is convertedinto plasma.

Example 3

While the above examples have been described with the single crystallinesilicon layer in the STI process, the etching method of thepolycrystalline silicon for forming the gate electrode will be describedhereinafter.

A wafer W used in this experiment is described with reference to FIG. 5.The wafer W was of a structure in which an oxide film 82 serving as agate oxide film, a polycrystalline silicon film 83, a resist film 84formed of, e.g., tetra ethyl ortho silicate (TEOS) were formed on asilicon layer 81 in that order from the bottom side. The resist film 84was provided with protruded portions 85 and openings 86. Further, asdescribed with reference to the wafer W shown in FIG. 1, there wereformed the first region, i.e. a dense pattern region in which theopening width S1 of the openings 86 was narrow and the protrudedportions 85 were densely arranged and the second region, i.e. a sparsepattern region in which the opening width S2 of the openings 86 waswide. Furthermore, the pattern was formed such that the dimension L ofthe protruded portions 85 was 100 nm and the opening widths S1 and S2 inthe dense and sparse pattern regions were respectively 160 nm and 1100nm. On the other hand, in case of a product wafer W, the polycrystallinesilicon film 83 would be doped with P (phosphorus) or B (boron). Herein,an experimental wafer W which was not doped was used. A space(corresponding to 14 in FIG. 1C) was formed under the same conditions asthose of the example 1 except for the following conditions.

[Processing Conditions]

Processing pressure: 4.0 Pa (30 mTorr)

Power of the upper electrode 40: 600 W

Power of the lower electrode 31: 100 W

Example 3-1

Processing gas: Cl₂/HBr/CO=500/100/10 sccm

Example 3-2

Processing gas: Cl₂/HBr/CO=500/100/20 sccm

Comparative Example 3

Processing gas: Cl₂/HBr=500/100 sccm

Experimental Result

As shown in FIG. 6, the result of processing the wafer W by adding COgas is the same as those of the above examples. Further, the etchingrate and the micro-loading are also immaterial. The data obtained by theabove experiments are shown in the following Table 1.

TABLE 1 Example 1 Example 2 Example 3 CO flow rate CO₂ flow rate CO flowrate (sccm) (sccm) (sccm) 0 10 20 0 20 40 0 10 20 Angle α 86.4 85.5 84.286.7 85.7 84 89.4 88.6 87.6 of β 84.3 84 83.4 84.7 84.1 83.6 88.5 8887.4 space α-β 2.1 1.5 0.8 2 1.6 0.4 0.9 0.6 0.2 14(87) (deg)Micro-loading 1.01 1.06 1.09 Etching rate 183 174 168 (nm/min)

Example 4

Preliminary experiments were performed before the above experiments inorder to check whether the effect of the etching method of the presentinvention could be obtained by changing the processing conditions and,hereinafter, the results thereof would be described. The preliminaryexperiments were performed on the wafer W shown in FIG. 1 with theintention that the tilt angles α and β of the lines 17 in the dense andsparse pattern regions were substantially identical and further the tiltangles α and β were reclined, i.e. smaller. The detailed experimentalconditions are omitted. The result is shown in Table 2.

TABLE 2 Absolute Difference values of the between the tilt angles tiltangles α and β Processing pressure X X Power of the lower ◯ X electrode31 Flow rate ratio of Cl₂ gas X X Flow rate of O₂ gas ◯ X Total gas flowrate X ◯ Temperature of the wafer W X ◯ Addition of CO gas ◯ ◯

Table 2 shows the result obtained when each parameter was increased.O-sign in the column of the absolute values of the tilt angles indicatesthat the tilt angles α and β decreased, whereas O-sign in the column ofthe difference between the tilt angles α and β represents that thedifference of the tilt angles α and β decreased. That is, O-signindicates a desired result in any cases.

From the result, it has been found out that both columns cannot beimproved at the same time by increasing any parameter. However, it isnoted that, by adding CO gas, the tilt angles α and β in the dense andsparse pattern regions became substantially identical and the tiltangles α and β became smaller.

Meanwhile, from Table 2, it may be inferred that the same result as thatof the present invention may be obtained by reducing the processingpressure or the flow rate ratio of Cl₂ gas. However, since the etchingrate is also significantly lowered by doing so, it is not preferable.

While the invention has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the invention as defined in the following claims.

1. An etching method for forming a groove by etching a silicon layer ofa substrate by using a mask which has a first region where an openingwith a first opening width is formed and a second region where anopening with a second opening width larger than the first opening widthis formed, the method comprising: mounting the substrate on a mountingtable in a processing chamber; converting a processing gas containingCl₂ gas, HBr gas, and one of CO gas and CO₂ gas into a plasma; andetching the silicon layer by the plasma to thereby make substantiallyidentical sidewall tilt angles of protruded portions between grooves ina first and a second etched region respectively corresponding to thefirst and the second region of the mask, wherein a flow rate of one ofthe CO gas and the CO₂ gas is controlled such that an added amount ofmicro-loading indicated as a ratio of a groove depth in the secondetched region to that in the first etched region is about 10% or lesscompared with a case of using neither the CO gas nor the CO₂ gas, andwherein the mask is patterned such that a ratio of the second openingwidth to the first opening width is about 6 or more.
 2. The etchingmethod of claim 1, wherein protruded portions between grooves aredensely arranged in the first region and are less densely arranged inthe second region than in the first region.
 3. The etching method ofclaim 1, wherein the mask is formed of a silicon nitride film.
 4. Theetching method of claim 1, wherein etching the silicon layer isperformed by converting the processing gas into the plasma by supplyinghigh frequency power between an upper electrode which is disposed abovethe substrate to face it and a lower electrode serving as a part of themounting table.
 5. The etching method of claim 1, wherein sidewall tiltangles of protruded portions between grooves in the etched silicon layerare controlled by adjusting an amount of carbon in the plasma bychanging a flow rate of one of the CO gas and the CO₂ gas.